More than 100 million people — almost one-third of the U.S. population — were in the path of a storm that started battering the Midwest and the East Coast with snow early Thursday. By late Thursday night, the National Weather Service said 21 in. of snow had fallen in a town just north of Boston. About 18 in. fell on parts of upstate New York, and New York City was bracing for heavy snowfall overnight and into Friday morning. Schools in Boston and state government offices in Massachusetts will remain closed on Friday as Gov. Deval Patrick advised residents to remain indoors and avoid “very, very dangerous” temperatures. New York Gov. Andrew Cuomo declared a state of emergency and ordered three major highways across the state shut, the Associated Press reports.

There were sub-zero windchill temperatures in New York City overnight and into Friday morning, and John F. Kennedy International Airport was closed.

Across the country, more 2,300 flights have been canceled and 7,000 delayed, according to the flight-tracking website FlightAware. New York’s Port Authority prepared hundreds of cots for travelers stranded in airports, according to Reuters. In Boston, authorities at Logan International Airport had already canceled or delayed dozens of flights, the Boston Globe reports. The airport’s last departure Thursday was scheduled for 8:30 p.m., and planes will not be brought in for scheduled Friday-morning flights. Boston authorities warned that up to 2 ft. of snow could accumulate in some places.

The National Weather Service issued a blizzard warning through Friday morning for the Northeastern U.S. on Thursday, warning that “falling and blowing snow with strong winds and poor visibility are likely. This will lead to whiteout conditions … making travel extremely dangerous.”

The warning contained a blunt piece of advice for those in the storm’s path: “Do not travel.”

The storm brought winter weather to parts of the country stretching from Illinois to the Eastern seaboard and Maine to North Carolina, with the harshest conditions expected in the area from West Virginia and Maryland to southern Maine, the Weather Channel reports. As the storm moves across the eastern U.S., temperatures in the region are plunging to below freezing, snarling transportation networks with up to a foot of snow in some places.

Residents of New York City braced for up to 12 in. of snow between Thursday evening and Friday morning, with wind chills as low as –10°F and temperatures expected to persist in the single digits into Saturday, CNN reports. Albany, in upstate New York, was facing up to 14 in. of snow and wind chills as cold as 25 below zero. The storm will be at its worst between 8 p.m. Thursday and 10 a.m. Friday.

Up to 11 in. of snow were predicted to fall on Chicago on Thursday, according to the National Weather Service, and more than 300 flights were canceled Thursday morning at O’Hare International Airport. As a central travel hub, O’Hare clocks in as the most affected airport by the storm. Newark’s Liberty International Airport, New York’s LaGuardia Airport and Cleveland’s Hopkins Airport are also among the most affected.

In the Midwest and southern U.S., the frigid air is expected to continue into next week. A blast of frigid wind broke record lows in Minnesota on Thursday and a second cold front will push farther south Monday and Tuesday bringing temperatures as low as zero as far south as Nashville.

Snow Covers Midwest and Northeast As Storm Rages

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A boy walks across the snow covered lawn in front of the Capitol Visitor Center at the U.S. Capitol in Washington, Jan. 3, 2014.